Centralized device for the control of the feeding voltage of a load provided with a power factor correction condenser

ABSTRACT

A centralized device for supply voltage control of a load with power factor correction condensers for lighting engineering applications has an array converter for obtaining a portion of power, with a plurality of switches located between the network sinusoidal supply and the load. The centralized device has controlling and regulating means for managing both the activation and deactivation states of the switches of the array converter so as to avoid sudden voltage changes across the load and provide for control of the load voltage.

The present invention relates to a centralized device for supply voltagecontrol of a load with power factor correction condensers, in particularfor lighting engineering applications, comprising a power portionobtained by means of an array converter, which comprises in turn aplurality of switching means, located between the network sinusoidalsupply and the load.

Street lighting systems, or those systems provided for large sport,industrial, commercial or educational areas, should be able to changetheir lighting power depending on their real utilization requirements,so as to obtain a considerable saving of electric power and extend lampslife.

Common systems for reducing the lighting power are based onelectromagnetic devices, such as transformers with sockets or VARIAC, oron the use of electronic controllers. Both cases are subject toutilization restrictions. In the instance of electromagneticcontrollers, these restrictions are basically ascribable to thedimensions and weights of the transformers; a further technicalrestriction is due to the limited number of applicable sockets to atransformer, hindering in the practice the possibility of controllingthe supply voltage output with a higher precision than a few percentpoints. In the instance of electronic controllers, two differenttechniques are used, i.e. the former providing generation of the outputvoltage through the gating of a set of amplitude modulated voltagesimpulses (PWM), the latter acting through application of a portion ofthe supply voltage to the load by means of the so-called phase controltechnique or also phase cut-off. Both solutions require application ofsudden voltage changes to the load, which hinder its use in the case ofimproved loads, i.e. fitted with optimising condensers of the powerfactor, which is a usual condition for high performance lamps with verylow power factors.

So far, electronic solutions have required the removal of the capacitivebehaviour of the load, or removal of the power factor correctioncondensers themselves, i.e. a method adopted when using phase cut-offcontrollers requiring a current increase of the system, or introducingappropriate filters, i.e. the method adopted for PWM controllers, whichrepresents again the problems of dimensions and weights as typical forthe electromagnetic solutions.

U.S. Pat. No. 4,456,855 discloses a light regulator, especially a lightregulator which is suitable for the regulation of the light intensity ofboth compensated and uncompensated illuminators connected to analternating-current mains, said regulator having one or a plurality ofswitch elements fitted in a circuit between the mains and theilluminator, as well as a control circuit for a switch element orelements which in the course of the regulation intensity switches offthe supply current at least once on each half cycle when the current hasbeen conducted from the 0-moment of a half cycle to the moment accordingto a set value.

The main disadvantage of U.S. Pat. No. 4,456,855 is that it does nottake into consideration the different behaviour of loads of differentnature, thus it does not permit a good regulation strategy.

It is the object of the present invention to solve the above drawbacksand provide a centralized device for supply voltage control of a loadwith power factor correction condensers, in particular for lightingengineering applications, which is improved and has a better performancecompared to common solutions.

In this frame, it is the main object of the present invention to providea centralized device for supply voltage control of a load with powerfactor correction condensers, in particular for lighting engineeringapplications, which is able to control the load voltage through a phasecut-off technique when using power factor correction condensers, withoutthe use of outlet filters, so the device can be applied to lightingsystems and manufactured according to standard criteria.

In order to achieve such aims, it is the object of the present inventionto provide a centralized device for supply voltage control of a loadwith power factor correction condensers, in particular for lightingengineering applications, incorporating the features of the annexedclaims, which form an integral part of the description herein.

Further objects, features and advantages of the present invention willbecome apparent from the following detailed description and annexeddrawings, which are supplied by way of non limiting example, wherein:

FIG. 1 shows a schematic view of a lighting system with a centralizeddevice for supply voltage control of a load with power factor correctioncondensers, according to the present invention;

FIG. 2 shows a basic schematics of the centralized device for supplyvoltage control of a load with power factor correction condensers,according to the present invention;

FIG. 3 shows a schematic view of the centralized device for supplyvoltage control of a load with power factor correction condensers,according to the present invention;

FIGS. 4 a, 4 b, 4 c, 4 d show a representation of the operation states,in particular a conduction state and locking state of the centralizeddevice for supply voltage control of a load with power factor correctioncondensers, according to the present invention.

FIG. 1 is representing a lighting system 10 comprising power supplyterminals 31 connected to a supply network, not illustrated. Thislighting system comprises a load 11, which is modelled and representedby a variable number of discharge lamps 11 a fitted with a feeder 12 andpower factor correction condenser 13. This load 11 is supplied by asingle-phase alternate voltage through the terminals 31.

The lighting system 10 comprises an electronic power device 14 locatedbetween the terminals 31 and the load 11 for controlling and choking thepower supplied to said load 11, according to requirements.

In FIG. 2, where the lighting system 10 of FIG. 1 is better detailed,the load consisting of multiple lamps 11 a is converted to an equivalentlamp also indicated with 11 a, for simplicity's sake.

According to the present invention, the electronic power device 14located between the terminals 31 and the load 11 consists substantiallyof an array converter 15, comprising two bi-directional switches 16 and17 interlaying between the terminals 31 and the load 11, connected inseries and in parallel to said load 11, respectively; the electronicpower device 14 also comprises a control and regulation system 18 forcontrolling the operation of said bi-directional switches 16 and 17.

Said electronic power device 14 operates according to a phase cut-offstrategy, i.e. connecting the load 11 to the supply network only in linewith the phase angles selected by the control and regulation device 18based on regulation requirements.

According to the present invention, the electronic power device 14operates according to a phase cut-off technique as mentioned above, i.e.indicating with 0° the through point for zero network voltage, while theelectronic power device 14 will maintain the load 11 connected to thesupply 31 for a portion only of the initial electric 180°of the sinecurve identifying the supply phase, so as to let power through betweenthe supply network itself and the load 11 according to one of thediagrams detailed in the FIGS. 4 a and 4 b. This operating procedure isrepeated in the subsequent electric 180°, i.e. it is applied to both thepositive half wave and negative half wave of the supply voltage.

The control and regulation system 18 calculates the exact time forinterruption of the connection between the power supply and the load 11,i.e. it operates the appropriate phase cut-off for obtaining the loadvoltage requested by the control phase and cause deactivation of thebi-directional switch 16 connected in series to the supply. As it can benoticed in FIG. 4 a, the bi-directional switch 16 consists of twounidirectional electronic switches 51 and 52, in particular separatelycontrolled transistors. Based on the network voltage and line currentmeasurements performed upstream by proper voltage sensors 19 anddownstream by the current sensors 20 and voltage sensors 21,communicating with three respective inlets Vin, Iin and Vout of thesystem 18, the control and regulation system 18 will select through theproper outlets C1 and C2 the electronic switch 51 or 52 of the switch 16to be deactivated for actual circuit interruption, with a consequentzero setting of the current on the load 11.

Now, both the supply voltage and load tension 11 will start a phase inwhich they evolve depending on their features. In particular, the supplyvoltage continues its standard sinusoidal trend with both the voltageand frequency established by the supply network, whereas the loadtension 11 undergoes an evolution as provided by the electric featuresof the load 11 itself.

Actually, three different voltage trends of the load 11 can bedescribed:

-   -   in the case of an ideally inductive load 11, said load 11 would        tend to maintain unchanged the current flowing through it,        causing a sudden change to the output voltage. In particular,        for a current flowing out of the load 11 the voltage would be        led towards negative values;    -   in the dual case of an ideally capacitive load 11, the load 11        itself would tend to maintain the voltage unchanged with respect        to the voltage corresponding to the time the circuit has been        interrupted;    -   in the case of an ideally resistive load 11, both the load        voltage and current would instantly go out as the main switch is        deactivated, and allow restart of the same mechanism in the        subsequent half cycle of the supply voltage.

As known, in real applications the load 11 has in intermediate behaviourbetween the inductive, capacitive and resistive behaviours. The controland regulation device 18 is provided for obtaining a condition at theend of each regulation cycle, which ensures a restart of the controlstrategy, as described in the example of an ideal resistive load. Inorder to obtain this situation, the device 14 has the bi-directionalswitch 16 connected in series to the supply and the furtherbi-directional switch 17 connected in parallel to the load 11, accordingto the diagram known as “array converter”.

As said above, the purposes of the switch 16 connected in series to thesupply is to connect the load 11 to the network, whereas the switch 17in parallel to the load 11 will provide an alternative path to thecurrent established by the inductive portion of the load 11 once theswitch in series 16 is open, in order to ensure control of anover-voltage caused by the load 11 itself.

In the device 14 according to the present invention special attention isgiven to the time a connection is executed between the load 11 and thesupply network, since both the supply network and converter 13 of theload 11 behave like ideal voltage generators during the connectiontransitory, both tending to establish the voltage to the remainingcircuit. In view of this feature, even small calculation faults from anelectric standpoint of the activation time, such as small voltagedifferences between the load 11 and the supply network, may lead touncontrolled current impulses incompatible with the devices forming thecircuit. For this reason all activations should be provided in advanceand the actual closure of the electric circuits always be caused by thenatural evolution of the circuit itself. The control and regulationdevice 18 is provided to this purpose, i.e. presetting activation of theswitch 51 or 52 at every regulation cycle, which is put in a conductionstate by the circuit voltages and currents. In other words, the controland regulation device 18 operates on the control terminal of thetransistors presetting them for conduction at the time the appropriatevoltage conditions are obtained on their emitters and collectors.

As it can be better noticed in FIG. 4 a, the switch in series 16consists of a transistor 51, whose collector is connected to the supplyand the emitter is connected to the emitter of a transistor 52, havingits collector connected to the load 11. The bases of said transistors 51and 52 are driven by the outlets C1 and C2 of the control and regulationdevice 18, respectively. Each transistor has a protection diode inparallel.

The switch in parallel 17 consists in its turn of a transistor 53, whosecollector is connected downstream to the switch in series 16, while theemitter is connected to the emitter of a transistor 54, having itscollector connected to the neutral. The bases of said transistors 53 eand 54 are driven by the outlets C3 and C4 of the control and regulationdevice 18, respectively.

As previously described, the load 11 consists of several elements, whichcan be schematised by the lamp 11 a, where the inductance 12 in seriesto the lamp 11 a is representing the feeder and a condenser 13 inparallel to the set described above is provided for raising the loadpower factor.

It is obvious how the behaviour of the circuit is depending on thebehaviour of all the elements forming it. These may change during thelamps and system life. In particular, the lamp 11 a increases the archvoltage during its life, with a consequent circuit impedance increase.During the system life the power factor correction condensers 13 undergoan ageing phenomenon, which reduces their capacity, whereas deactivationof a lamp or interruption of its circuit due to a burnt-out power supplyor operation of a protection fuse, appears like an increase of thecapacitive features of the load for the voltage regulator.

FIGS. 4 a, 4 b, 4 c and 4 d illustrate the conduction and lockingconditions established by the control and regulation device 18 throughthe bi-directional switches 16 and 17. As it can be noticed in FIG. 4 a,the transistor 51 of the switch in series 16 is activated to let thecurrent I through between the network and the load, while the transistor52 is by-passed by means of the protection diode. On the contrary, thetransistors 53 and 54 of the switch in parallel 17 remain deactivated.

In FIG. 4 b, the transistor 52 of the switch in series 16 is activatedfor the current I to flow between the load and the network, while thetransistor 51 is by-passed by means of the protection diode. Thetransistors 53 and 54 of the switch in parallel 17 remain deactivated.

In FIG. 4 c, the transistor 54 of the switch in parallel 17 is activatedfor the current I to flow from the neutral to the load, whereas thetransistor 53 is by-passed by means of the protection diode. Thetransistors 51 and 52 of the switch in parallel 16 remain deactivated.

In FIG. 4 d, the transistor 53 of the switch in parallel 17 is activatedfor the current I to flow from the load to the neutral, whereas thetransistor 54 is by-passed by means of the protection diode. Thetransistors 51 and 52 of the switch 16 in parallel remain deactivated.

In order to include all variables due to both the behaviour of the load11 and current conduction possibilities of the device 14 in the aboveregulation strategy, the control and regulation device 18 has threedifferent operating procedures, i.e. one for the loads having mainlyinductive features, one for mainly capacitive loads and one forintermediate loads typical of the operation states with phasedifferences maintaining the power factor around the unity, which formthe base of the control system called Adaptive Waveform Intersection(AWI).

Based on the voltage and current measurements through the sensors 19, 20and 21, the regulation device 18 can automatically select the mostcorrect operating procedure between the three above procedures andestablish a correct through flow from one operation procedure to theother, always warranting a consistent supply to the load 11.

Capacitive mode: after the circuit interruption caused by the device 16,the voltage of the load 11 tends to maintain itself consistent. Withreference to the positive half wave of the supply voltage, thisevolution may cause a higher load voltage than the supply voltage; as aresult, a sudden change of the load voltage would be required to bringboth voltages back to the same value, with a consequent gating of acurrent impulse unacceptable for the electronic components. In order toavoid this situation, the control and regulation device 18 will firstdeactivate the unidirectional switch 51 conducting current according tothe diagram of FIG. 4 a and activate (FIG. 4 b) the unidirectionalswitch 52 (both switches forming the switch in series 16); so, as soonas the load voltage tends to become higher than the network voltage,said transistor 52 becomes conductive according to the diagram of FIG. 4b, providing a circuit to let the current through between the load 11and the network, as required.

Similarly, an exchange of the conduction conditions in the negative halfwave also takes place between the diagrams of the FIGS. 4 b and 4 a.

Inductive mode: After the circuit interruption, the current through theload 11 tends to remain consistent. With reference to the positive halfwave of the supply voltage, such an evolution may cause the load voltageto reach even higher negative values as an absolute value than thesupply voltage itself. In order to avoid this situation, the control andregulation device 18 will first deactivate the unidirectional switch 51conducting current according to the diagram of FIG. 4 a, and activate(FIG. 4 c) the unidirectional switch 54, which is able to conduct thecurrent in the direction of the load current. Thus, the voltage on theload 11 is maintained around zero; at the subsequent passage for zerosupply voltage, the device 14 can execute again a connection between thesupply and the load without the risk of voltage differences.

Similarly, an exchange of the conduction conditions in the negative halfwave also takes place between the diagrams of the FIGS. 4 b and 4 a.

As mentioned above, a connection between the supply network and the loadcannot occur forcedly; therefore, it is necessary in line with thepassage for zero supply voltage that the control and regulation devicewill activate the switch in series 16, conducting the supply voltage inthe subsequent regulation cycle and deactivate the switch in parallel 17conducting the current of the load 11 at a subsequent time only. Oncethe switch in parallel 17 is deactivated, the voltage of the load 11evolves according to the conditions of the inductive, capacitive andresistive features of the load itself and starts conduction of one ofthe switches 51, 52 connected in series to the load previouslyactivated. The free evolution of the load voltage starting from zerovalue for highly inductive loads may occur with a higher gradient thanfor the line voltage around zero value; therefore, advanced deactivationof the switch in parallel 17 with respect to the passage for zero supplyvoltage would cause higher values to the load voltage than the networkvalues, with the consequent risk of a load voltage overelongation beforethe switch in series 16 returns to its conduction state. For this reasondeactivation of the switch 17 in parallel to the load occurs after thepassage for zero supply voltage. This phase is particularly delicate,due to a possible short-circuit between the supply phase and theneutral, typical for the diagrams utilizing array converters. Thecontrol and regulation device 18 is advantageously provided forestablishing a state of the four transistors 51, 52, 53, 54 hinderingthis event.

Vice-versa, if deactivation of the switch 17 in parallel is delayed toolong compared to the passage for zero network voltage, a condition canbe reached during which no transistor will be conducting during thecontrol cycle. This condition is detected by the control and regulationdevice 18, which causes a forced passage to an intermediate operationfor the subsequent cycle, as described hereafter. In order to avoid thisunusual operation mode, where no transistor is starting conduction, thecontrol and regulation device 18 verifies at each cycle the phaseshifting condition between the supply voltage and load current, thusbeing able to decide in advance the passage from the inductive mode tothe intermediate mode.

Intermediate mode: the intermediate mode is quite similar to theinductive one; its substantial difference consists in being suitable forthose situations where the load voltage gradient is smaller or equal tothe gradient of the supply voltage after deactivation of the switch inparallel to the load itself. In this case, deactivation of the switch 17in parallel occurs in advance compared to the passage for zero supplyvoltage, so the load voltage will equal the supply voltage during thesubsequent regulation cycle. Through the measurement of the outputvoltage the control and regulation device 18 verifies no overvoltagesarise on the load voltage due to the free evolution of the latter, andin case of a such measured voltage increase it causes the passage to theinductive operation mode. The sequence of the conduction states,similarly to the inductive operation mode, is 4 a, 4 c, 4 b, 4 d.

FIG. 3 is illustrating a detailed diagram of the control and regulationdevice 18, which provides input information about the network voltage,load current and voltage through the sensors 19, 20 and 21. Saidinformation is sent to a selection block 41 of the operation mode,deactivation control block 42 and switching logic block 43. Blocks 41and 42 control the block 43, which supplies the signals to the outletsC1, C2, C3, C4 for controlling the switches 16 and 17.

Based on the measured quantities, the block 41 detects the correctoperation mode between the capacitive, inductive and intermediate mode,and supplies this information to the switching logic 43.

Based on the measured quantities, the block 42 calculates the phaseangle for deactivation of the switch 16 in line with it and communicatesit to the switching logic 43.

Based on the electric quantities, selected operation mode anddeactivation time of the bi-directional switch 16, the switching logic43 generates the activation controls C1, C2, C3 and C4 and thedeactivation controls for the switches 51, 52, 53 and 54, respectively.

Thus, with the subsequent selection of the various operation modes andaccording to the so-called AWI system, the regulation device 18 ensuresthe control of the voltage applied to the load by means of the phasecut-off strategy. The amplitude of this cut-off is calculated by thecontrol following a reference signal, which can be obtained by a requestof operation voltage or through elaboration of a luminous sensor signalaccording to the type of lighting system under control.

From the above description the features of the present invention areclear, and also its advantages are clear.

The centralized device for supply voltage control of a load with powerfactor correction condensers, in particular for lighting engineeringapplications according to the present invention, advantageously ensuresvoltage control of the load with power factor correction condensersthrough the so-called AWI system, without using output filters, so thedevice itself can be applied to lighting systems designed andmanufactured according to standard criteria. Actually, the use oftransistor switches in an array converter structure driven by a suitablecontrol system will advantageously adapt the converter structure to boththe operation mode and transistors occurring in line with the phasecut-off operations.

It is obvious that many other changes are possible for the man skilledin the art to the centralized device for supply voltage control of aload with power factor correction condensers, in particular for lightingengineering applications, described above by way of example, withoutdeparting from the novelty principles of the inventive idea, and it isalso clear that in practical actuation of the invention the componentsmay often differ from the ones described above, and be replaced withtechnical equivalent elements.

For instance, the transistors indicated as switching means can bebipolar transistors, MOSFET or any other electronic controlled switch.

1. A centralized device for supply voltage control of a load with powerfactor correction condensers for lighting engineering applications,comprising: a power portion including an array converter, which has aplurality of switching means located between the network sinusoidalsupply and the load, and controlling and regulating means for managingthe activation and deactivation states of said switching means of saidarray converter, thus avoiding application to the load of sudden voltagechanges and ensuring control of continuous voltage values of the load,wherein said controlling and regulating means are connected to sensingmeans from which they receive information on the values reached by theload voltage and current and supply voltage, and in that, based on thevoltage and current measurements through said sensing means, saidcontrolling and regulating means can automatically select the mostcorrect operating procedure between a set of operating procedures.
 2. Acentralized device for supply voltage control of a load with powerfactor correction condensers for lighting engineering applicationsaccording to claim 1, wherein said set of procedures consists of threepredetermined operating procedures.
 3. A centralized device for supplyvoltage control of a load with power factor correction condensers forlighting engineering applications according to claim 1 wherein one ofsaid operating procedures is for the loads mainly capacitive features.4. A centralized device for supply voltage control of a load with powerfactor correction condensers for lighting engineering applicationsaccording to claim 1 wherein one of said operating procedures is for theloads having mainly inductive features.
 5. A centralized device forsupply voltage control of a load with power factor correction condensersfor lighting engineering applications according to claim 1 wherein oneof said operating procedures is for the intermediate loads.
 6. Acentralized device for supply voltage control of a load with powerfactor correction condensers for lighting engineering applicationsaccording to claim 4 wherein said controlling and regulating means areadapted to said information received from the sensing means, thus beingable to decide in advance the passage from the operating procedure forthe mainly inductive loads to the procedure for the intermediate loadsand vice-versa.
 7. A centralized device for supply voltage control of aload with power factor correction condensers for lighting engineeringapplications according to claim 1 wherein said switching means of saidarray converter comprise electronic controlled switches.
 8. Acentralized device for supply voltage control of a load with powerfactor correction condensers for lighting engineering applicationsaccording to claim 7, wherein said switching means comprise a switchconnected in series between the supply and the load and a switchconnected in parallel to the load.
 9. A centralized device for supplyvoltage control of a load with power factor correction condensers forlighting engineering applications according to claim 8, wherein each oneof said switching means comprise at least two transistors connected toeach other by means of their emitters and provided with protectiondiodes.
 10. A centralized device for supply voltage control of a loadwith power factor correction condensers for lighting engineeringapplications according to claim 7 wherein said controlling andregulating means operate the control electrodes of said transistorsthrough special signal outlets.
 11. A centralized device for supplyvoltage control of a load with power factor correction condensers forlighting engineering applications according to claim 1, wherein saidcontrol and regulation device comprises an operation mode selectionblock and a deactivation control block, which receive information fromthe sensing means on the values reached by the load voltage and/orcurrent and/or supply voltage, through special inlets of said controland regulation device.
 12. A centralized device for supply voltagecontrol of a load with power factor correction condensers for lightingengineering applications according to claim 11, wherein said operationmode selection block and deactivation control block control a switchinglogic block driving the plurality of outlets for controlling theswitches.
 13. A centralized device for supply voltage control of a loadwith power factor correction condensers for lighting engineeringapplications according to claim 12, wherein said switching logic blockidentifies the correct operation mode between the capacitive, inductiveand intermediate modes, based on the measured quantities, supplying saidinformation to the switching logic block.
 14. A centralized device forsupply voltage control of a load with power factor correction condensersfor lighting engineering applications according to claim 12, whereinsaid block calculates the phase angle in correspondence to withdeactivation of the switch has to be performed, based on the measuredquantities, communicating it to said switching logic block.
 15. Acentralized device for supply voltage control of a load with powerfactor correction condensers for lighting engineering applicationsaccording to claim 13 wherein said switching logic block drives theactivation and deactivation outlets for the transistors, respectively,based on the electric quantities, selected operation mode and upondeactivation of said bi-directional switch.
 16. A method for controllingthe supply voltage of a load with power factor correction condenserswhich provides for the use of a switch structure in the form of an arrayconverter, said method controls said supply voltage operating a phasecut-off strategy, and provides for controlling and regulating means forthe execution of said strategy, wherein, in order to actuate a switchingof said switches, said method provides for: receiving information on thevalues reached by the voltage and current of the load and supplyvoltage; and automatically selecting the most correct operatingprocedure between a set of operating procedures.
 17. A method forcontrolling the supply voltage of a load with power correctioncondensers according to claim 16, wherein said controlling andregulating means operate for obtaining a condition at the end of eachregulation cycle such to ensure restart of the control strategy, as ifin the instance of an ideal resistive load.
 18. A method for controllingthe supply voltage of a load with power correction condensers accordingto claim 17, wherein said controlling and regulating means operate acontrol according to a capacitive mode, maintaining the transistor thathas not interrupted the supply current activated between two transistorsforming the switch connected in series, so that as soon as the loadvoltage tends to become higher than the network voltage, a circuit willlet the required current through between the load itself and thenetwork.
 19. A method for controlling the supply voltage of a load withpower correction condensers according to claim 18, wherein saidcontrolling and regulating means operate a control according to theinductive mode, activating the transistor connected in parallel to theload between the two transistors forming the switch, being able toconduct current in the direction of the load current, in order tomaintain the voltage on the load around zero and let the device executea connection again between the supply and the load at the subsequentpassage for zero supply voltage, without a risk of voltage differences.20. A method for controlling the supply voltage of a load with powercorrection condensers according to claim 19, wherein said controllingand regulating means activate the switch connected in series forconducting the supply current to the subsequent regulation cycle, andwill subsequently deactivate the switch connected in parallel conductingthe current of the load.
 21. A method for controlling the supply voltageof a load with power correction condensers according to claim 20,wherein in the event of no transistors starting conduction during thecontrol cycle, said control and regulation device will cause a forcedpassage to an intermediate operation mode for the subsequent cycle. 22.A method for controlling the supply voltage of a load with powercorrection condensers according to claim 20, wherein said intermediatemode operates analogously to the inductive mode; however, deactivationof the switch connected in parallel occurs in advance compared to thepassage for zero supply voltage, so that the loading voltage will equalthe supply voltage during the subsequent regulation cycle.